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Unread 08-27-2014, 05:11 PM   #1
TnKanRick
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Great Day! Got my CJ7 to start. Now I have a tach wiring question

I recently did a dash rehab / reinstallation and couldn't get my Jeep to start after the reinstall. I added an aftermarket Crown tach to the dash. The instructions for the Crown tach said not to use the factory tach wiring. So, I removed the factory tach wire going to the distributor side of the coil and hooked the Crown tach to the distributor side of the coil.

I've spent the last few days trying to figure out why the Jeep would no longer start and it turns out that removing the factory tach wire from the coil was the reason. Once I hooked the factory tach wire back up to the coil the Jeep started right up. So now I have a quandary. Do I hook both the Crown tach wire and the factory tach wire to the coil. I'm sorta afraid if I do it will fry my Crown tach.

Anybody know for sure?

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Unread 08-27-2014, 05:31 PM   #2
LumpyGrits
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What's wrong with the OEM Tach?
Much better than Crown--
LG
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Unread 08-27-2014, 05:39 PM   #3
OrangeCJ-5
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Sounds to me like he never had one which is why he 'added an aftermarket Crown tach to the dash.'
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Unread 08-27-2014, 05:43 PM   #4
LumpyGrits
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Originally Posted by OrangeCJ-5 View Post
Sounds to me like he never had one which is why he 'added an aftermarket Crown tach to the dash.'
That is possible-
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Unread 08-27-2014, 06:03 PM   #5
keith460
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Factory tachometer never hooked up to the coil, it is in "series" with the ignition wiring. A wire plug gets pulled apart under the dash to connect the factory tach.

A crown tachometer connects as like any other aftermarket tachometer does. 12V+, Grd and Coil tach (-) for signal which is green. Plus another wire for dash lighting which I believe is white in color.
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Unread 08-27-2014, 06:19 PM   #6
TnKanRick
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Quote:
Originally Posted by keith460 View Post
A crown tachometer connects as like any other aftermarket tachometer does. 12V+, Grd and Coil tach (-) for signal which is green. Plus another wire for dash lighting which I believe is white in color.
Yes, my Jeep did not have a factory tach but nonetheless has the factory wiring for a tach. Should I attach both the factory tach green wire and the Crown tach green wire to the (-) side of the coil?
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Unread 08-27-2014, 08:14 PM   #7
keith460
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Mmm, not sure what you mean? There is no green wire for a factory tachometer to connect to the coil.

Are you planning on using two tachometers? One factory and one aftermarket.

Back of factory tach pictured, no green wire. Just red w/tracer and an orange that connect to factory ignition plug under dash and a black and orange for lighting.
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Unread 08-27-2014, 08:21 PM   #8
Requiem4aCJ
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Quote:
Originally Posted by TnKanRick View Post
Yes, my Jeep did not have a factory tach but nonetheless has the factory wiring for a tach. Should I attach both the factory tach green wire and the Crown tach green wire to the (-) side of the coil?
the only factory wire connected to the (-) post of the coil is the wire from the ignition module that tells the coil when to fire, if you disconnect this the engine doesn't run. So yes leave it connected and attach the wire for your new tach with it.
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Unread 08-27-2014, 08:44 PM   #9
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That part of the instructions about removing the factory tach is only applicable if you had a factory tach to begin with. No factory tach = no tach wire at the coil, but there are other wires as already noted.
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Unread 08-27-2014, 09:19 PM   #10
ThisGuyUKnow
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The crown tach hooks up to the negative side of your coil. I believe it's the green wire. I bought one to use with my 4.0 swap and it didn't work initially, I had to set the back to 4cyl to get it to work. I'm not sure if that is the same for the 258 set up.
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Unread 08-28-2014, 07:05 AM   #11
TnKanRick
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Thanks guys. That all makes sense now. I made the assumption (yes... rarely a good idea) that the "tach side of the coil" meant that the only thing that could possibly be attached to that side were tach related wires. As Homer Simpson would say.... "DOOH!" I'm seriously red-green colorblind which makes working on wiring that much more of a challenge.... especially in low or artificial light conditions. Thanks again for all the help and replies.
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Unread 10-14-2014, 09:56 PM   #12
mapesful
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I recently bought a 85 CJ7 and the previous owner removed the dash and all the gauges completely. Would the tachometer cause my jeep not to start?
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Unread 02-19-2015, 05:28 PM   #13
jjgrow
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Originally Posted by keith460 View Post
Plus another wire for dash lighting which I believe is white in color.
Dumb question, but where do we connect this white tach illumination wire? I've installed an OEM-style tach and just need to connect to the dash light circuit.
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Unread 02-19-2015, 05:53 PM   #14
John Strenk
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I believe it went into the fuse box originally.


There is a plug called CLK with a little arrow, left side next to the 10 amp ACC fuse.
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Unread 02-19-2015, 05:54 PM   #15
John Strenk
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Quote:
Originally Posted by mapesful View Post
I recently bought a 85 CJ7 and the previous owner removed the dash and all the gauges completely. Would the tachometer cause my jeep not to start?
If it had a factory tach then yes, Just unpluging it would prevent the engine from running
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